The invention relates to a dispensing system for depositing discrete amounts of adhesives on a surface. More particularly, the system monitors and controls the amount of adhesive deposited on a surface to which a microcomponent is secured.
In electronics many assembled parts are exceedingly small such that vision systems are necessary to view the movement, placement and securing of the parts one to the other. Securing of the parts usually includes bonding by solder or adhesives. In some applications, the parts are pretreated by coating with a solder or adhesive, engaging the parts and then being cured by heat. These bonding techniques are suitable for components that once assembled remain static except possibly for the flow of electrons. In some applications the assemblies are subjected to varying mechanical stresses during curing process. In this environment, a thin film coating of adhesive is usually not sufficient. One such component that is subject to stress is a read-write slide which is secured to a supporting resilient arm. In a typical application, one end of the supporting arm is fastened to a base. The other end or the arm supports the read-write slide. The head is joined to the other end of the arm by adhesive, usually a drop of epoxy adhesive.
Epoxy dispensing systems for joining a read-write slide to a supporting arm are currently in use. The average deposit of epoxy on the arm will vary between 2 to 8.times.10.sup.-6 cubic inches. Typically, the deposits are discharged through an orifice in timed sequence or manually.
The amount to be deposited is initially calibrated. Once a dispensing system is calibrated, the viscosity and rheology of the adhesive may change with temperature and with time. Also the homogenity of the adhesive is not always uniform. The adhesive may include dissolved gases. However, with the small amounts involved, slight temperature changes will affect the physical properties of the adhesive. If the deposit becomes too small, an incomplete bonding results. If the deposit becomes too great, the bond may be sufficient but because of the size and delicate nature of the assembly, the excess adhesive can interfere with the proper functioning of the assembly. Therefore, dispensing systems which depend upon a fixed pulsed displacement of adhesive by the precalibrated movement of a piston or the like are subject to variations in the amounts of adhesive dispensed.
Our invention overcomes these problems of variations in the amounts of deposited adhesive by optically controlling the amount of adhesive dispensed from an orifice. The adhesive is discharged through an orifice but does not contact a target surface. The amount of adhesive depending from the orifice is continuously monitored by a vision system. When the amount or size of adhesive depending from the orifice is within pre-established limits, the adhesive is then transferred to the target surface.
In a preferred embodiment, a camera system views the amount of the adhesive extruded from the orifice. Based on this information, the adhesive stops flowing or continues to flow through the orifice until the proper amount is reached. At this time, the flow ceases and some of the adhesive is transferred. The amount of adhesive which remains depending from the orifice after transfer is measured to ensure the correct amount was transferred. Therefore, our invention overcomes the problems inherent with those systems where the adhesive is subject to variations in viscosity and homogenity.
Our invention, in a preferred embodiment, comprises flowing an adhesive through an orifice, measuring the amount of adhesive being extruded from the orifice, stopping the flow of adhesive through the orifice when a predetermined amount of adhesive has been extruded and transferring the adhesive to a target site, measuring the amount of adhesive remaining on the orifice after transfer and confirming the amount transferred was within pre-established limits.